What if we cannot agree on our child custody arrangement?

The court will decide for you. You should try to work it out. Negotiation is always better than imposition. If you leave it up to the court to decide, you are including the element of surprise. You can never tell what a judge may decide and you may discover that it is neither what you, your spouse, or your child(ren) desire. No one understands your family better than you and/or your spouse, so to leave the decision(s) up to a judge is often a regrettable option.